Yaf_Loader attempt to load a class only one shot, if
failed, depend on yaf.use_spl_auload, if this
config is On Yaf_Loader::autoload() will return
FALSE, thus give the chance to other autoload function. if it is Off
(by default), Yaf_Loader::autoload() will return
TRUE, and more important is that a very usefull warning will be triggerd
(very usefull to find out why a class could not be loaded).

Note:

Please keep yaf.use_spl_autoload Off unless there is some library have
their own autoload mechanism and impossible to rewrite it.

By default, Yaf_Loader assume all library (class
defined script) store in the global library
directory, which is defined in the php.ini(yaf.library).